Engineers gave the space shuttle Atlantis a crucial clean bill of health for landing on Thursday, but clean hardly describes the area of cosmic clutter the shuttle is leaving. The more astronauts looked outside on Wednesday, the more they found bits of floating debris they had accidentally dumped. But the trash didn't damage the shuttle, and NASA was all slightly sheepish smiles after a bit of a worry.
"Sorry, we're being a litterbug here," shuttle program manager Wayne Hale said.
Two sightings of baffling pieces of debris on Tuesday worried NASA enough to delay Atlantis' landing so that Wednesday could be spent inspecting the shuttle's critical, delicate heat shield. Three new mystery objects turned up during that work.
No damage was found, but "this stuff came from the shuttle," Hale said.
NASA is aiming for a 6:21 am EDT (1021 GMT) landing attempt at the Kennedy Space Centre in Florida with a crystal clear weather forecast.
"We are cleared for entry, nothing was found to be missing or damaged on the thermal protection system, the heat shield of the space shuttle Atlantis or in fact any other part of the space shuttle Atlantis," Hale said on Wednesday. "So we feel we're very confident that we're in good shape for a landing opportunity." For Atlantis, the crucial cosmic math is this: a 17 1/2-ton addition connected to the international space station; three spacewalks; five mysterious pieces of space junk; two bolts that floated away during the spacewalks; two last-minute inspections; one extra day in space and "zero defects on the heat shield," Hale said. "That is really the bottom line."
Damage to the space shuttle Columbia's heat shield led to its 2003 disintegration during landing. So NASA is now more cautious about any potential hits to the shuttle's tiles or leading edges. "We've seen a new standard in NASA vigilance," Hale said.
John Logsdon, a member of the independent board that investigated the Columbia accident, praised NASA for being "prudent" in taking the extra day to make sure everything is safe.
After the initial debris discovery, Atlantis' 11-day mission was extended so the six astronauts could use the shuttle's robot arm and a 50-foot (15-meter) extension boom to give the shuttle two top-to-bottom inspections.
While Atlantis' crew slept, engineers on the ground operated cameras on the shuttle robot arm to check out the cargo bay and flight control systems. When the astronauts woke up, they had to do the harder part of moving the shuttle's arm for the first 4 1/2-hour inspection and then the arm-and-boom for a two-hour examination of harder-to-see places.
"It was a long day, especially for Fergie and Dan," Atlantis commander Brent Jett radioed Mission Control, referring to pilot Chris Ferguson and astronaut Dan Burbank, who operated the robotic arm. "But you do what you need to do. We understand everybody's doing the right thing, so we're happy to do what it takes." Astronauts went to sleep early they were so tired. If Atlantis can't land at 6:21 am EDT (1021 GMT), it can try again at 7:57 am EDT (1157 GMT).
Atlantis' complex mission—resuming construction on the international space station with a 17 1/2-ton addition—sputtered to get off the ground with four technical and weather launch delays and caused concerns before landing. But in between those hassles, the mission itself went off nearly flawlessly.
On Wednesday, NASA managers concentrated more on the health of the shuttle's heat shield than on trying to figure out what the objects were that dirtied the area around Atlantis. Hale said his best guess the first object that set off NASA's alarms was an orange plastic filler placed in between thermal tiles that protect the shuttle from blasting heat. A second mystery object was spotted several hours later, midday on Tuesday, by Burbank; Hale said it appeared to be a garbage bag.
During Wednesday's inspections, the astronauts spotted three more pieces of floating debris. Jett described the objects as two rings and a piece of foil. He told Mission Control the first object, about 100 feet (30 meters) from the shuttle, was "a reflective cloth ... It's not a solid metal structure."
NASA officials said space junk coming from space flights and space walks is a constant problem.
"Clearly we have more work to do" to reduce space littering, Hale said. "It's on the to-do list. It's probably not on the top of the to-do list."